Light emitting devices, such as light emitting diodes (LEDs) for example, are often packaged within surface mounted device (SMD) housings. These housings are often made of plastic and can be referred to as plastic leaded chip carriers (PLCCs). SMD housings typically feature an LED chip connected to multiple metal leads formed from a leadframe and can optionally comprise a heat slug. Current packages comprise portions of the metal leads which extend outside of the package and protrude from one or more lateral sides of the body. The increased surface area of the extended leads increase the capacity of the LED package to dissipate heat, however, the extended leads increase the size of the LED package requiring a relatively large area on a circuit board. Circuit board area is a scarce and costly factor in many applications. In addition, the extended leads require more metal during package fabrication which can increase overall package cost.
Examples of prior art LED packages are illustrated by FIGS. 1A-1B and 2A-2B. Referring to FIGS. 1A and 1B, a LED package, generally designated 10, has a body 12 typically formed from molded plastic, ceramic, thermoset, and/or thermoplastic materials. Body 12 includes four lateral sides 1-4, a bottom surface 5, and a reflector cavity 14. An encapsulant E fills the reflector cavity 14 to a desirable level, typically flush with the top of the reflector cavity. Encapsulant E typically contains a phosphor for producing a desired wavelength spectrum. Located along a bottom floor of the reflector cavity are electrical components, typically metal leads 16 and 18 formed from a leadframe, and to which one or more LED chips 20 are electrically connected. LED chips 20 can optionally be mounted to a heat slug 22 which is electrically and thermally isolated from the metal leads 16 and 18 by insulating portions 24 and 26, respectively, of the body 12. Heat slug 22 can improve thermal properties, including heat dissipation of LED package 10.
Conventional designs for packages having metal leads 16 and 18 utilize portions of the leads which extend outside or external to the plastic body in addition to portions which are encased or molded within the body. For example, FIG. 1B is a cross-sectional view along line 1B in FIG. 1A. FIG. 1B illustrates body 12 which is molded about portions of metal leads 16 and 18 and portion of the heat slug 22. External portions 28 and 30 of leads 16 and 18, respectively, protrude from and extend away from lateral sides 4 and 2 and beyond the outermost edges of the body 12. Metal leads 16 and 18 are separated from the leadframe by terminating, such as by shearing, the external ends 34 and 36 of the leads 16 and 18 from the leadframe. External portions 28 and 30 have a bend 32 which can configure the external portions 28 and 30 to extend away from each other and away from the body 12. As illustrated by FIG. 1B, this design utilizes metal leads 16 and 18 which differ in thickness, and are typically thinner with a smaller cross-sectional area than the heat slug 22. Heat slug 22 protrudes from bottom surface 5 of the body 12 and metal leads 16 and 18 protrude from lateral sides 2 and 4 of the body 12. All three of heat slug 22 and metal leads 16 and 18 become mounted to an external circuit source, generally a printed circuit board (PCB), at a location where they protrude from the body. For example, heat slug 22 comprises bottom surface 37 and metal leads 16 and 18 comprise bottom surfaces 38 and 39, respectively. These bottom surfaces are mounted to the PCB typically by using solder technology. In addition, the metal leads 16 and 18 have portions which are embedded on all four sides of the LED package 10. For example, metal leads 16 and 18 can be embedded but extend from the body at external portions 28 and 30 on two opposing sides of LED package 10, and can be embedded and flush with the remaining two opposing sides within the LED package 10. As such, the metal forming the metal leads 16 and 18 is located on all four sides of the LED package 10. Because the leads 16 and 18 contain portions 28 and 30 that extend from the body externally at lateral sides 2 and 4, extra processing steps of bending the metal leads causes LED package 10 to have both an increased cost and a larger footprint than necessary thereby increasing the amount of space needed on a PCB.
Referring to the prior art package illustrated by FIGS. 2A-2B, this design features an LED package generally designated 40, having a body 42 with lateral sides 1-4 and a bottom surface 5. This package design also features a reflector cavity 44 configured for receiving a desirable level of encapsulant E. In this package design, body 42 is molded about a first metal lead 46 and a second metal lead 48, wherein second metal lead 48 has a portion formed by stamping the metal to form a metal cup 50. Metal cup 50 forms metal walls about an inner bottom surface 51a located or disposed on a lower and different plane P2 than a surface of the body 42 forming one insulating portion 54 of the body which can be located or disposed on plane P1. Metal cup 50 forms one electrical contact upon which one or more LED chips 52 are mounted. In addition to forming an electrical contact, cup 50 also serves as the thermal element, or heat slug, and is thereby neither electrically nor thermally isolated from both metal leads 46 and 48. Cup 50 is thermally and electrically isolated from the first metal lead 46 by insulating portion 54 of the body. Cup 50 protrudes from bottom surface 5 of the body 42 to form an exposed portion 51b while first and second metal leads 46 and 48 have external portions 56 and 58, respectively which protrude from lateral sides 2 and 4 and extend beyond the outermost edges of the body 42. The first and second metal leads 46 and 48 are separated from the leadframe by shearing the external ends 47 and 49 from the leadframe. The external portions 56 and 58 of first and second metal leads 46 and 48, respectively, have external bends 60 and 62 which transition the external portions 56 and 58 to bend and/or wrap about body 42 such that they extend towards and face each other while also bending in towards metal cup 50. External portions 56 and 58 are disposed in recesses 64 and 66 of bottom surface 5 of body 42 to enable bottom surfaces 68 and 70 of external portions 56 and 58 to rest flush with and adjacent to the exposed portion 51b of the metal cup 50. These bottom surfaces are mounted to the PCB typically by using solder technology. As LED chip 52 is not thermally isolated from both first and second metal leads 46 and 48, the external source, for example the PCB will have to supply the isolation when connecting the LED package 10 components in series. For example, first and second metal leads 46 and 48 are thin and have a small cross-sectional area. For this reason, capacity of the metal leads to remove heat from the LED is limited. This limits the amount of power that can be sent to LED chips thereby limiting the amount of light that can be generated by the LED package. This design is similar to the design illustrated by FIGS. 1A and 1B as external portions 56 and 58 of first and second metal leads 46 and 48 thereby increases the footprint, includes a difficult bending step for the external portions, and increases the amount of metal necessary to fabricate the package which in turn increases cost and decreases space available on a PCB. In addition, this design utilizes metal leads 46 and 48 having portions which are embedded on all four sides of the LED package 40. For example, metal leads 46 and 48 are embedded but extend from the body at external portions 56 and 58 on two opposing sides of LED package 40, and are embedded and flush with the remaining two opposing sides within the LED package 40. As such, the metal forming the metal leads 46 and 48 is located on all four sides of the LED package 40.
Consequently, there remains a need for improved LED packages that overcome or alleviate shortcomings of prior art packages.